Semiconductor structure, HEMT structure and method of forming the same

Abstract

A semiconductor structure includes: a channel layer; an active layer over the channel layer, wherein the active layer is configured to form a two-dimensional electron gas (2DEG) to be formed in the channel layer along an interface between the channel layer and the active layer; a gate electrode over a top surface of the active layer; and a source/drain electrode over the top surface of the active layer; wherein the active layer includes a first layer and a second layer sequentially disposed therein from the top surface to a bottom surface of the active layer, and the first layer possesses a higher aluminum (Al) atom concentration compared to the second layer. An HEMT structure and an associated method are also disclosed.

What is claimed is: 
     
       1. A semiconductor structure, comprising:
 a channel layer; 
 an active layer over the channel layer, the active layer includes a first layer at the top surface and a second layer directly under the first layer at a bottom surface thereof, the first layer possessing a higher aluminum (Al) atom concentration compared to the second layer, and a ratio of a primary peak for Al atom concentration in the first layer to an Al atom concentration in the second layer is from about 1.1 to 2.5. 
 
     
     
       2. The semiconductor structure of  claim 1 , wherein the active layer includes a group III-V compound. 
     
     
       3. The semiconductor structure of  claim 1 , wherein the first layer has a thickness of about 1 nm to about 5 nm. 
     
     
       4. The semiconductor structure of  claim 1 , wherein a two-dimensional electron gas (2DEG) is formed in the channel layer along an interface between the channel layer and the active layer. 
     
     
       5. The semiconductor structure of  claim 1 , wherein the primary peak for Al atom concentration is located in the active layer and is distanced below the top surface of the active layer. 
     
     
       6. The semiconductor structure of  claim 5 , wherein the primary peak for Al atom concentration is located at the first layer. 
     
     
       7. The semiconductor structure of  claim 1 , wherein the first layer is blanket disposed at a top of the active layer. 
     
     
       8. The semiconductor structure of  claim 1 , further comprising a source/drain electrode and a gate electrode, wherein the source/drain electrode is laterally distanced from the gate electrode by a first lateral distance, the first layer is partially disposed at a top of the active layer and is kept from the gate electrode by a second lateral distance, wherein a ratio of the second distance to the first distance is from about 0 to about 0.8. 
     
     
       9. The semiconductor structure of  claim 8 , further comprising a gate dielectric between the gate electrode and the active layer. 
     
     
       10. A high electron mobility transistor (HEMT) structure, comprising:
 a channel layer; and 
 an extra aluminum (Al) diffused active layer over the channel layer, wherein the extra Al diffused active layer includes a high Al diffusion film at a top surface of the extra Al diffused active layer, wherein the high Al diffusion film possesses a higher Al atom concentration compared to a remaining portion of the extra Al diffused active layer beneath the high Al diffusion film; 
 a gate electrode over the top surface of the extra Al diffused active layer; and 
 a source/drain electrode over the top surface of the extra Al diffused active layer, wherein the gate electrode is distanced from the source/drain electrode by a first distance, and the gate electrode is distanced from a nearest end of the high Al diffusion film at the side of the source/drain electrode by a second distance, and a ratio of the second distance/the first distance is from about 0 to about 0.8. 
 
     
     
       11. The HEMT structure of  claim 10 , further comprising a semiconductor substrate, wherein the channel layer is over the semiconductor substrate. 
     
     
       12. The HEMT structure of  claim 11 , further comprising a transition structure between the semiconductor substrate and the channel layer. 
     
     
       13. The HEMT structure of  claim 10 , further comprising a gate dielectric between the gate electrode and the active layer. 
     
     
       14. The HEMT structure of  claim 10 , wherein the channel layer includes gallium nitride (GaN). 
     
     
       15. The HEMT structure of  claim 10 , wherein the extra Al diffused active layer includes aluminum gallium nitride (AlGaN). 
     
     
       16. The HEMT structure of  claim 10 , wherein the high Al diffusion film includes AlGaN. 
     
     
       17. The HEMT structure of  claim 10 , wherein a ratio of a primary peak for Al atom concentration in the high Al diffusion film to an Al atom concentration in the extra Al diffused active layer is from about 1.1 to 2.5. 
     
     
       18. A high electron mobility transistor (HEMT) structure, comprising:
 a channel layer; 
 a first extra aluminum (Al) diffused active layer over the channel layer; and 
 a second extra Al diffused active layer over the first extra Al diffused active layer and overlapping a first portion of the first extra Al diffused active layer and free from overlapping a second portion of the first extra Al diffused active layer; 
 wherein the second extra Al diffused active layer includes a higher aluminum (Al) atom concentration compared to the first extra Al diffused active layer. 
 
     
     
       19. The HEMT structure of  claim 18 , wherein the first extra Al diffused active layer and the second extra Al diffused active layer include aluminum gallium nitride (AlGaN). 
     
     
       20. The HEMT structure of  claim 18 , further comprising a gate dielectric between a gate electrode and the first extra Al diffused active layer, the gate dielectric being arranged to form a non-ohmic contact to an upper surface of the first extra Al diffused active layer.